Fixing Font Configuration Warning Messages

Solved:
Having multiple <family> in
<alias> isn't supported and
may not work as expected

I started seeing a lot of these warning messages
when I upgraded to the latest
OpenBSD release.
But I have also seen reports of this in various Linux
distributions.
Things work — our music starts playing,
or our browser starts,
or our network protocol analyzer comes up ready to capture
packets, but these font warning messages are annoying.

Some troubleshooting becomes more tedious,
as even more clutter is thrown into
~/.xsession-errors
while programs starts.
What causes these font configuration warning messages,
and how can we fix the underlying problem?

The Cause

Fonts are configured through files under
/etc/fonts/.
The specific files and directories are:

/etc/fonts/fonts.conf

This master configuration file tells the X font server
where to find the font definitions, probably in
/usr/X11R6/lib/X11/fonts/
or similar.

It also works around the possible use of some
outdated directives, such as deprecated
mono instead of new monospace,
and alternative
sans and sans serif instead of
sans-serif,
and possibly others.

/etc/fonts/conf.d/

This directory is filled with the fontconfig
configuration files that will be used.

It is usually filled with symbolic links
pointing to the font configuration files.
The idea is that you install a large number of fonts
and then create symbolic links only to those that work.

This directory is scanned and the files named
[0-9][0-9]* are used in order.
That is, those files with names starting with two digits.
The naming convention is: